The stellar content of the new "faint" dwarf spheroidals (dSphs) discovered around M31 can provide fundamental
insight to reconstruct the star formation history and the merging episodes that led to the assembling of the M31 halo.
We present results from our study of the variable stars and stellar populations in the And IX dwarf spheroidal companions of M31,
based on g', r' time-series photometry we obtained on October-November 2010, as part of our ESO Large Program 186.D-2013 at
GTC (PI G. Clementini).
Several tens RR Lyrae stars were discovered in And IX and well sampled light curves were obtained out of our 23 epoch data,
with accuracy of the individual epoch data better than 0.1 mag even at the RR Lyrae minimum light, which is around g'~25.5 mag.
The RR Lyrae stars allowed us to firmly establish the galaxy distance and get a glimpse of the early history of this recent
addition to the census of the M31 satellites. Our CMD for And IX reaches g'~26.3-26.4 mag, this is 1 mag fainter than
presently available in the literature. It shows a prominent red giant branch (RGB) and the horizontal branch (HB) is clearly visible at
g'~25.3 mag altough rather contaminated by field stars.